The present invention relates to a thermally conductive sheet used for a countermeasure against heat of electronic components, particularly to a thermally conductive sheet composite and a method of manufacturing the thermally conductive sheet composite of which consideration is given to the delivery form and the ease of handling of the thermally conductive sheet.
For example, on electronic components such as CPUs mounted on electronic devices, a heat radiating body such as a heat sink is installed in order to cool the electronic components, which are heat generating bodies. In order to promote thermal conduction from a heat generating body to a heat radiating body, a thermally conductive sheet is sandwiched between the heat generating body and the heat radiating body. Utilization of a thermally conductive sheet increases the thermal conduction area between a heat generating body and a heat radiating body, and allows heat to escape from the heat generating body to the heat radiating body.
In a thermally conductive sheet, the conformability and adhesion to a heat generating body and a heat radiating body decrease the thermal resistance value, which is an index indicating the unlikeliness of heat transfer, thereby improving the thermal conduction performance. From this viewpoint, more flexible thermally conductive sheets are preferably used. However, a more flexible thermally conductive sheet exhibits a higher adhesion. Therefore, in some cases, sheets are adhered to each other when a plurality of the sheets are stored in a stacked state, and attaching work of a sheet on a heat generating body involves a difficulty due to the adhesion of the sheet. On the other hand, a thermally conductive sheet that is thinner gives a more improved thermal conduction. From this viewpoint, thinner thermally conductive sheets are preferably used. However, making thinner the shape of thermally conductive sheets having the flexibility and adhesion results in further decrease in the ease of handling of the thermally conductive sheets.
For example, Japanese Laid-Open Patent Publication No. 2-196453 discloses a thermally conductive sheet composite provided with a first silicone resin layer that is easily deformable and a second silicone resin layer that is laminated on the first silicone resin layer and has a strength necessary for handling. Japanese Laid-Open Patent Publication No. 10-183110 discloses a manufacturing method of a thermally conductive sheet composite obtained by preparing a pair of resin films whose surfaces are coated with a rubber composition, sandwiching a silicone gel blended with a thermally conductive filler between the films, further rolling both films between a pair of rolls, and finally curing them through a heating furnace. The thermally conductive sheet has a rubbery thin film reinforcing layer on at least one surface thereof. Japanese Laid-Open Patent Publication No. 11-307697 discloses a thermally conductive sheet composite provided with a silicone rubber layer A containing a thermally conductive filler and having a Shore A hardness of 20 or more, and a silicone rubber layer B containing a thermally conductive filler and having an Asker C hardness of 30 or less.
Additionally, from the viewpoint of manufacture, transportation, attachment and the like, a thermally conductive sheet composite containing a gelatinous thermally conductive sheet and resin films laminated on both surfaces of the thermally conductive sheet is commercially available. When using a thermally conductive sheet composite of such a type, the resin films are peeled off the thermally conductive sheet at the point of use and only the thermally conductive sheet can be pasted on the surface of a heat generating body or a heat radiating body. Therefore, the gelatinous thermally conductive sheet can bring the heat generating body and the heat radiating body into close contact, and provide excellent thermal conduction and low thermal resistance.
However, the sheet composites disclosed in the documents described above are formed by simultaneously molding and curing a gelatinous thermally conductive sheet and a rubbery reinforcing sheet for reinforcing the thermally conductive sheet. That is, since the thermally conductive sheet and the reinforcing sheet constituting the sheet composite are integrated, the reinforcing sheet cannot be peeled off the thermally conductive sheet at the point of use. Therefore, since these thermally conductive sheet composites have excellent ease of handling, but by contrast, have low adhesion to a heat generating body and a heat radiating body, there is a room for improvement in their thermal conduction.
As sheet composites used by peeling a resin film off, ones which are formed as a relatively large area sheet material, and cut into a predetermined shape and size depending on applications are provided from the viewpoint of productivity, mass productivity and the like. In this case, a gelatinous thermally conductive sheet is cut into a predetermined shape and size together with a resin film by using a cutter or the like. However, when using a sheet composite of such a type, if the hardness of the thermally conductive sheet is made further low in order to improve the adhesion to a heat generating body or a heat radiating body, the gelatinous thermally conductive sheet together with the resin film is difficult to cut. Specifically, as shown in FIGS. 11A and 11B, if a thermally conductive sheet 50 is cut together with a resin film 51, the flexibility of the thermally conductive sheet 50 causes the thermally conductive sheet 50 to be crushed along its cut portions C. This varies the shapes of the end parts of the thermally conductive sheet 50, which may cause errors in sizes such as area and thickness of the thermally conductive sheet 50 after being cut.
Other than sheet composites described above, a constitution is conceivable in which a gelatinous thermally conductive sheet is previously cut into a predetermined shape and size according to applications and the thermally conductive sheet after being cut is pasted on a release sheet. However, such a constitution takes much labor for cutting of the thermally conductive sheet, pasting it to a release sheet and the like, and requires much time, which may increase the manufacturing costs.